Bandwidth management in modem high speed packet communications networks utilizes connection level controls applied at the time the connection is set up based on the load characteristics of the transmission links in the connection route at the time that the connection is set up. Such connection level controls include bandwidth allocation, path selection, admission control and call setup. Bandwidth allocation is accomplished by noting, at the connection setup time, the "equivalent capacity" loading that the new connection will generate, based on the traffic characteristics of the source signal and the desired quality of service. Using this equivalent capacity as the bandwidth that must be available to carry the new connection, the originating node of the network computes a path to the destination node that is capable of carrying the new connection and providing the level of service required by the new connection. This path selection process utilizes data describing the current state of the traffic in the entire network. Such data can be stored in a topology database located at each entry point, and, indeed, at each node, of the network. If no suitable path can be found to meet these requirements, the connection is rejected. Once a suitable path has been selected at the entry node, a setup message is generated which traverses the selected route, updating the resource allocations for each link visited by the setup message. Due to race conditions, simultaneous requests for setup, or unknown changes in the link resource allocation, the attempt to set up the call may fail because of the lack of necessary resources at the time the call setup message reaches a node along the route. In general, each connection level control process, i.e., initial bandwidth allocation, route selection and call setup, requires adequate network resources to carry the call. A failure at any point in any of these control processes results in the call being rejected, thus preventing the launching of packets likely to cause network overload.
It is essential to successful traffic management and a congestion-free network that the connection level controls operate correctly at all times. Furthermore, in order to efficiently accommodate connections for data streams with widely different characteristics, it is important to allocate bandwidth for each connection with a metric which is readily computable, easily updated and capable of capturing all of the significant characteristics of the highly diversified traffic. Moreover, this metric must also be used to characterize the accumulated transmission link traffic load due to all of the individual connections on that link, determined by a simple additive process from the individual connection vectors. An easily calculated additive metric to characterize traffic on a network is a critical factor for efficient traffic control in the network.
The copending application of the present applicant, and others, Ser. No. 07/932,440, filed Aug. 19, 1992, discloses a metric for both the new connections and for all of the existing traffic on a network, utilizing a link metric vector for each link in the connection. Using statistical multiplexing techniques, the capacity of each link in a proposed route is examined to determine if the new connection can be handled on a statistical basis. A new link metric for the link with the new connection is then the simple vector addition (or subtraction, for disconnect requests) of the connection link vector. The efficiency of these link metric values is, of course, dependent on the enforcement of an access control mechanism that enforces these values.
The algorithm for computing link metrics disclosed in the aboveidentified patent application is computationally efficient, readily allowing for real-time updates of the link metric vectors while, at the same time, accounting reasonably well for the relationship between the link bandwidth and the connection characteristics. This algorithm also preserves the incremental nature of the link metric updates so that information on the individual connections need not be maintained in the network topology database.
Unfortunately, the assumption in the above-identified patent application that all classes of traffic can be adequately accounted for by a single link metric is true only if all of the classes of traffic have similar quality of service requirements. In fact, however, traffic can have very different requirements, particularly in the priority assigned to the data packets in each class. Real-time traffic (e.g., voice and video), for example, should always take priority over non-real-time traffic (e.g., accounting information). That is, real-time traffic demands very small transmission delays, and therefore requires a much greater bandwidth allocation. Using the same link metric for all classes of data can severely reduce the overall throughput of the network since all of the traffic must conform to the same priority treatment. It is therefore often necessary to reserve significantly more bandwidth than is actually required to handle the lower priority classes of traffic when using this prior art single link metric.